Many functions, particularly functions such as telecommunications functions requiring filters, audio amplifiers, and the like need precise gain stages. These functions typically may be combination digital and analog circuits on a single monolithlic semiconductor substrate.
A conventional operational amplifier with a resistive feedback element and a resistive input element provides gain as a function of the ratio of the feedback resistor to the input resistor. In the design of integrated circuits, however, resistors have relatively poor processing tolerances. The poor tolerances of the resistors result in inaccuracies in the gain of such amplifier stages. To overcome the poor tolerance of integrated circuit resistors, circuits which require extreme precision have relied upon external components, the use of which is otherwise undesirable because of the requirement for additional pins on the integrated circuit package and the necessary additional space on the printed circuit board or other mounting means which contains the circuit of the particular function.
It is an object of the instant invention to provide an improved amplifier with an accurate gain which does not require the use of resistive elements to establish the gain of the amplifier.